This invention relates to a finely particulate amorphous porous inorganic substance and its sol; a process for synthesizing the same; use of the same; inkjet recording media containing the same, which are used for inkjet printing or recording, such as papers, sheets, films, and fabrics; and a coating liquid used to produce the inkjet recording media.
Technologies using fine inorganic particles attract attention not only from expectation for improved functions of electronic materials but also from the standpoint of energy saving and environmental conservation.
Known fine inorganic particles, which are mostly produced by a vapor phase method or a liquid phase method, include oxides, such as Aerosil and colloidal silica, and metal particles, such as colloidal gold. Most of them are solid particles with no pores inside. On the other hand, known amorphous porous inorganic substances include gels with pores between grains, such as silica gel and alumina gel, and amorphous activated carbon, which are generally large particles.
Known amorphous porous inorganic fine particles include fine spherical porous silica particles disclosed, e.g., in JP-B-4-70255, but such a technique merely provides those having irregularly-shaped and small-diameter pores. Porous inorganic fine particles synthesized by using a template include those disclosed in Chem. Lett., (2000), 1044, Stu. Sur. Sci. Catal., 129 (2000), 37, and JP-A-11-100208, but all of them are crystalline. Substances with a regular structure exhibiting crystallinity are not always favorable for use as an adsorbent or a catalyst carrier on account of their shape selectivity. Further, there was obtained a precipitate in each case, and a sol having fine particles dispersed therein has not yet obtained. Examples of an amorphous porous inorganic substance obtained using a template include those disclosed in JP-A-2000-109312. However, the synthesis disclosed therein is carried out by a precipitation method using a combination of a metal silicate and an inorganic acid, and hence the product has a large particle size and is not obtained in the form of sol.
Inkjet recording has been extending its use in wide fields because of low noise, color recording capabilities, and high-speed recording capabilities. Since wood-free paper, etc. that are used in general printing are inferior in ink absorptivity, ink drying properties and image quality such as resolution, improved dedicated papers have been proposed to solve these inferiorities. Recording papers coated with various inorganic pigments including amorphous silica to have improved ink color developability or reproducibility have been disclosed (see, e.g., JP-A-55-51583 and JP-A-56-148585). However, along with recent progress of the performances of inkjet printers, further improvements have been demanded also on recording media and a satisfactory performance is not necessarily obtained merely with the above-described technique. In particular, obtaining high image quality equal to silver halide photographs involves increases of the ink ejection amount per unit area of a recording medium, which gives rise to insufficient ink absorptivity and blurring problems. Further, transparency of an ink absorbing layer has also been demanded for realizing high image quality and color density comparable to silver halide photographs.
The present invention is to provide an amorphous porous inorganic substance having a small particle diameter and a uniform pore shape, a sol thereof, and a synthesis process therefor.
Also, the present invention is to provide use of the substance, particularly an inkjet recording medium excellent in ink absorptivity and transparency, and a coating liquid for inkjet recording media.
The present invention provides the followings:
(1) A porous substance comprising inorganic particles which are amorphous and have pores of a uniform diameter,
wherein said particles have an average particle size DL of 10 to 400 nm as measured by a dynamic light scattering method, and
wherein said porous substance has a specific surface area difference, SBxe2x88x92SL, between a conversion specific surface area SL calculated from DL and a nitrogen adsorption specific surface area of the particles SB obtained by the BET method, of 250 m2/g or more.
(2) The porous substance set forth in item (1), wherein the pores have an average diameter of 6 nm or larger.
(3) The porous substance set forth in item (1) or (2), wherein the inorganic material is silicon oxide.
(4) The porous substance set forth in item (1) or (2), wherein the inorganic material contains silicon and aluminum.
(5) A sol comprising a solvent and 0.5 to 30% by weight of the porous substance set forth in any one of items (1) to (4) contained in the solvent.
(6) A porous substance sol comprising inorganic particles which are amorphous and have uniform pores and which are produced by a process comprising the steps of:
mixing a metal source comprising a metal oxide and/or a precursor thereof, a template, and water to prepare a metal oxide/template composite sol; and
removing the template from the composite.
(7) The porous substance sol set forth in item (6), wherein the process further comprises the step of adding an alkali aluminate.
(8) The porous substance sol set forth in item (6) or (7),
wherein the template is a nonionic surface active agent represented by structural formula (1):
HO(C2H4O)axe2x80x94(C3H6O)bxe2x80x94(C2H4O)cHxe2x80x83xe2x80x83(1)
wherein a and c each represent 10 to 110; and b represents 30 to 70, and
wherein the metal source, template and water are mixed at a water to template (water/template) weight ratio ranging from 10 to 1000.
(9) The porous substance sol set forth in any one of items (6) to (8), wherein the metal source and the template are mixed at a pH ranging from 3 to 12.
(10) The porous substance sol set forth in any one of items (6) to (9), wherein the metal source is active silica.
(11) The porous substance sol set forth in item (10), wherein the metal source, template and water are mixed at a weight ratio of the template to the active silica as the metal source in terms of SiO2 (template/SiO2) ranging from 0.01 to 30.
(12) A porous substance obtained from the porous substance sol set forth in any one of items (6) to (11).
(13) An inkjet recording medium comprising a support and one or more ink absorbing layers provided on the support,
wherein at least one of the ink absorbing layer(s) contains the porous substance set forth in any one of items (1) to (4) and (12).
(14) A coating liquid for an inkjet recording medium containing the porous substance and/or the porous substance sol set forth in any one of items (1) to (12).